Tricalcium orthophosphate, Ca.sub.3 (PO.sub.4).sub.2, commonly known as calcium phosphate, occurs in nature as rock phosphate ore, for example and is used as such as a source of fertilizer. It can also be converted with sulphuric acid to a mixture of calcium sulphate and phosphoric acid, or it can also be converted with sulphuric acid to a mixture of calcium sulfate and monocalcium phosphate, Ca(H.sub.2 PO.sub.4).sub.2, the latter also being known as calcium dihydrogen phosphate. Calcium phosphate has a relatively low phosphorous content (20% m/m) while monocalcium phosphate, while having a much higher phosphorous content (26.5% m/m), is difficult to manufacture, and also expensive mainly because one of the by-products of the reaction by means of which it is so prepared, calcium sulphate, has to be discarded as a waste product.
Dicalcium phosphate, CaHPO.sub.4, also known as calcium hydrogenphosphate, has a relatively high phophorous content (22.8% m:m) and may be used as a fertilizer. It is also used in animal licks as well as in the manufacture of certain toothpastes.
Therefore, there is a need in the art for an economical method of producing calcium hydrogenphosphate from calcium phosphate. There is a further need in the art for an economical method of producing monocalcium phosphate fertilizer from calcium phosphate and further producing edible products from the resultant fertilizer.